Wall Square Footage Calculator
Calculate the square footage of the walls in a room from its length, width and ceiling height, minus doors and windows, for paint, drywall, wallpaper or tile.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Wall square footage
- 366 sq ft
- After deducting 50 sq ft for 1 door and 2 windows
- Gross wall area
- 416 sq ft
- 52 ft perimeter x 8 ft ceiling height, before openings. Drywall, wallpaper and tile are bought from this number
- Long walls (2)
- 224 sq ft
- Each 14 ft x 8 ft, before openings
- Short walls (2)
- 192 sq ft
- Each 12 ft x 8 ft, before openings
- Perimeter
- 52 ft
- 2 x (Length + Width), the total length of wall
Wall Square Footage formula
Perimeter = 2 x (Length + Width)
Gross wall area = Perimeter x Ceiling height
Wall square footage = Gross wall area - (Doors x 20) - (Windows x 15)
Ceiling area = Length x Width (add it when the ceiling is being covered too)Worked example
An 11 x 13 ft bedroom with 9 ft ceilings, two doors and one window: the perimeter is 2 x (11 + 13) = 48 ft, so the gross wall area is 48 x 9 = 432 sq ft. Deduct 2 x 20 = 40 sq ft for the doors and 15 sq ft for the window: 432 - 55 = 377 sq ft of wall. The two long walls are 2 x 13 x 9 = 234 sq ft and the two short walls are 2 x 11 x 9 = 198 sq ft.
If the ceiling is being painted as well, add 11 x 13 = 143 sq ft, for 520 sq ft of walls plus ceiling.
Quick reference
| Room size | Perimeter | Gross wall area | After openings |
|---|---|---|---|
| 10 x 10 ft | 40 ft | 320 sq ft | 270 sq ft |
| 10 x 12 ft | 44 ft | 352 sq ft | 302 sq ft |
| 12 x 12 ft | 48 ft | 384 sq ft | 334 sq ft |
| 12 x 14 ft | 52 ft | 416 sq ft | 366 sq ft |
| 12 x 15 ft | 54 ft | 432 sq ft | 382 sq ft |
| 14 x 16 ft | 60 ft | 480 sq ft | 430 sq ft |
| 15 x 20 ft | 70 ft | 560 sq ft | 510 sq ft |
| 20 x 20 ft | 80 ft | 640 sq ft | 590 sq ft |
How to measure the walls in a room
Measure the length and width along the baseboards and the height in a corner, where the tape stands straight on the hard floor; over carpet it reads short. For a rectangular room, the perimeter times the height is the gross wall area. Rooms with alcoves, closets that open into the room, or a bay window are easier wall by wall: each wall's length times the height, added up. This is wall area for finish materials. It has nothing to do with the ANSI Z765 floor area on a listing, which appraisers measure at the floor and which never counts walls.
Sloped ceilings and stair walls are triangles or trapezoids: average the shortest and tallest heights and multiply by the length. A gable wall is a rectangle plus half the width times the rise. Round up to the next 10 sq ft. Paint sells by the gallon at 350 to 400 sq ft, so 5 sq ft never changes the order and 40 sq ft might.
When to deduct doors and windows
For paint, deduct the openings for material. Twenty square feet per door and 15 per window is close enough for a 3 ft door and a 3 x 5 window. Measure anything over about 30 sq ft, such as a 6 ft slider (40 sq ft), a picture window or a garage door. Painters estimating labor leave openings under about 100 sq ft in the count, because cutting in around casing takes longer than rolling the wall it replaces.
For drywall, wallpaper and tile, most estimators skip small openings entirely. The pieces cut out for a window or door are waste, not usable stock, so the gross wall area is the number to buy from. Deduct only openings larger than about 32 sq ft, the size of a full sheet. Wallpaper is sold by the double roll, nominally 56 sq ft but about 44 to 48 usable after the pattern repeat, so divide gross wall area by the usable figure.
What this calculator leaves out
Trim, doors and casings, closet interiors and the ceiling unless you add it. Paint is figured at 350 to 400 sq ft per gallon per coat, so double the area for two coats and add PVA primer on new drywall. The result is finish area only; it is not the living area a listing or appraisal reports (ANSI Z765), which is measured at the floor and requires a 7 ft ceiling to count.
Mistakes that cost money
- Using the listing's square footage: ANSI Z765 floor area says nothing about walls, which run 2.5 to 3 times the floor area at 8 ft.
- Deducting a 6 ft slider as one window drops about 25 sq ft; measure any opening over 30 sq ft instead of using the allowance.
- Buying drywall or wallpaper from the net area runs short because the cutouts are waste; those trades buy from the gross wall area.
- Measuring height over carpet or along a bowed wall reads 1 to 2 in off; stand the tape in a corner on the hard floor.
- Pricing labor with openings deducted underbids the job; painters keep openings under 100 sq ft in the count because cutting in is slower than rolling.
- A stairwell wall measured at ceiling height misses the triangle above the stairs; average the low and high heights times the run.
Key facts
- A standard interior door is 80 in tall and 30 to 36 in wide, about 20 sq ft with its casing.
- An average window is counted as 15 sq ft; a picture window or sliding patio door can be 40 sq ft or more, so measure those separately.
- Standard ceiling height in US homes is 8 ft; 9 ft ceilings are common on the first floor of newer houses and add 12.5% more wall area.
- A 12 x 12 ft room with 8 ft ceilings has 384 sq ft of gross wall area, about 334 sq ft after one door and two windows.
- Wall square footage drives most finish estimates: a gallon of paint covers 350 to 400 sq ft and a 4 x 8 sheet of drywall covers 32 sq ft.
Frequently asked questions
How do I calculate the square footage of a wall?
Multiply the wall's length by its height. A 14 ft wall under an 8 ft ceiling is 112 sq ft. For a whole room, multiply the perimeter by the height: a 12 x 14 ft room has a 52 ft perimeter, so 416 sq ft of wall.
Should I subtract doors and windows from wall square footage?
For paint, yes: about 20 sq ft per door and 15 per window, which takes a 12 x 14 ft room from 416 to 366 sq ft. For drywall and wallpaper, most estimators skip small openings because the cutouts end up as waste anyway.
Can I use my home's square footage to figure out how much paint I need?
No. The square footage on a listing is ANSI Z765 floor area, measured at the floor, and it says nothing about wall area. As a rough check, interior walls run 2.5 to 3 times the floor area with 8 ft ceilings, but measure each room; a 1,200 sq ft house can have 3,000 to 3,600 sq ft of wall.
Does wall square footage include the ceiling?
No. Add length times width if the ceiling is being covered too. A 12 x 14 ft room adds 168 sq ft, for 534 sq ft of walls plus ceiling after openings.
Sources and references
Next steps for this project
- Wall Square Footage
- Drywall
- Joint Compound
- Primer
- Paint
- Ceiling paint
- Paint Cost
The usual order for a paint & walls project. See all paint & walls calculators.
Embed this calculator
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.